A method for calculating carbon emission intensity of sewage pipe network based on anaerobic reaction theory

Abstract

The present invention provides a method for calculating the carbon emission intensity of a sewage pipe network based on the anaerobic reaction theory, comprising the following steps: S1, determining the biochemical reaction process of organic matter in the sewage pipe; S2, calculating the carbon emission intensity of the water body by the chemical reaction equation; S3: experimentally determining the water quality and key parameters required for the calculation; S4, calculating the carbon emission intensity of the sediment by the anaerobic endogenous respiration reaction equation; S5, determining the key parameters of the sediment endogenous model by laboratory simulation experiments; S6, calculating the overall carbon emission intensity of the pipe network based on the anaerobic reaction process. The present invention can be used for carbon emission accounting of sewage pipe networks under different boundary conditions, and compared with the emission factor method and the actual measurement method, it has stronger applicability and higher accuracy.

Description

Technical Field

[0001] The present invention belongs to the field of ecological environment protection, and specifically relates to a method for calculating the carbon emission intensity of a sewage pipe network based on anaerobic reaction theory. Technical Background

[0002] The drainage network collects sewage and transports it to the sewage treatment plant through drainage pumping stations and deep underground drainage pipes to remove pollutants and prevent the city from being harmed by pathogens and pollutants in sewage. However, with the development of urbanization, direct carbon emissions caused by sewage networks have gradually become an urban environmental problem that cannot be ignored. As the country vigorously promotes the pollution control measures of "reducing pollution and carbon emissions, and synergizing and increasing efficiency", sewage collection and treatment systems have gradually been included in the key links of carbon reduction plans. The CO generated by sewage networks 2 and CH 4 It is one of the carbon reduction targets of the environmental protection department. However, the existing methods cannot well calculate the direct carbon emission intensity of the sewage network.

[0003] Overview of existing carbon emission intensity calculation methods: 1. Emission factor method: This method mainly estimates the total amount of pollutants based on the population, formulates carbon emission factors in different fields, and then calculates carbon emission intensity. For example, the invention patent with announcement number CN116628410A discloses a method for calculating the carbon emission intensity of a regional power system. This method can use the carbon emission factor to calculate the total carbon emissions and carbon emission intensity generated by the electricity in the target area. 2. Actual measurement method: It mainly uses on-site CO 2 and CH 4 The data is collected and offline or online concentration analysis is performed to calculate the carbon emission intensity. For example, the invention patent with the announcement number CN116519876A discloses a method, device, equipment and storage medium for monitoring the carbon emission intensity of a thermal power unit. The method can use the baseline oxygen concentration data, the historical operation data of the unit and the current operation data of the unit to calculate the historical carbon emission intensity data of the unit and the current carbon emission intensity data of the unit.

[0004] The above existing accounting methods are still insufficient for studying the carbon emission intensity of sewage pipe networks: 1. The hydraulic and water quality elements in the sewage pipe network are complex and diverse. It is difficult to formulate emission factors under different boundary conditions when using the emission factor method to calculate the carbon emission intensity of the sewage pipe network. 2. The sewage pipe network is deeply buried underground and spread all over the city. If the actual measurement method is used to calculate the carbon emission intensity of the sewage pipe network, it is necessary to use a gas monitoring device to measure the CO in the pipeline. 2 and CH 4 The concentration is measured over a long period of time, which consumes a lot of manpower and material resources. In addition, the sewage pipe network exchanges gas with the outside air through the inspection well, and it is difficult to accurately measure the carbon emission intensity using conventional gas monitoring devices. Summary of the invention

[0005] 1. Problem to be solved

[0006] In view of the problem that the emission factor method and the actual measurement method are difficult to calculate the carbon emission intensity of the sewage network, the present invention adopts the material balance method and, based on the anaerobic reaction theory, proposes a method with strong applicability that can accurately calculate the carbon emission intensity of the sewage network.

[0007] 2. Technical solution

[0008] In order to solve the above problems, the technical solution adopted by the present invention is as follows:

[0009] S1: Determine the biochemical reaction process of organic matter in the sewage pipe;

[0010] S2: Calculate the carbon emission intensity of water bodies by chemical reaction equation;

[0011] S3: Experimentally determine the water quality and key parameters required for calculation;

[0012] S4: Calculate sediment carbon emission intensity using the anaerobic endogenous respiration reaction equation;

[0013] S5: Laboratory simulation experiments to determine the key parameters of the sediment endogenous model;

[0014] S6: Calculate the overall carbon emission intensity of the pipeline network based on the anaerobic reaction process.

[0015] Preferably, the step S1 specifically includes: determining the pollutant components in the sewage pipe, mainly including the content of sugar, protein and oil pollutants, and their chemical formulas, and determining the biochemical reaction process of the sewage pipe in the area according to the chemical formula.

[0016] Preferably, the step S2 is specifically as follows: anaerobic reaction of sewage refers to the process of decomposing various complex organic substances in sewage into substances such as methane and carbon dioxide by anaerobic microorganisms (including facultative anaerobic microorganisms) under the condition of no molecular oxygen. Some organic substances in sewage participate in anaerobic reaction to generate methane, and some organic substances are used for the growth of microorganisms themselves. n H a O b N c )The general chemical reaction formula of the anaerobic reaction process can be expressed as

[0017]

[0018] The symbols and values ​​in brackets in the above formula are the equilibrium coefficients of the reaction.

[0019] Where: d = 4n + a-2b-3c;

[0020] s—part of the organic matter converted into microorganisms;

[0021] e—Part of the organic matter converted into methane.

[0022] Theoretically, s+e=1. The s value varies with the organic matter composition, microbial community structure and metabolic activity. The specific value can be determined based on laboratory simulation experiments or estimated based on the following formula:

[0023] s=0.2a e

[0024] Where: 0.2—microorganism non-degradable coefficient;

[0025] a e —The maximum coefficient of conversion of organic matter into microbial microorganisms.

[0026] Anaerobic reactions of several pollutants e The values ​​(ratios based on COD) are shown in Table 1.

[0027] Table 1 Anaerobic reaction of several pollutants e value

[0028]

[0029] The total organic carbon concentrations at the inlet and outlet of the sewage network are TOC in and TOC out , the conversion coefficients are S in and S out , organic matter (C n H a O b N c ) The reduction can be calculated by TOC reduction and conversion coefficient, Δm = S in ·TOC in -S out ·TOC out . By organic matter (C n H a O b N c ) relative molecular weight, converted into the amount of substance N = Δm / (12n+a+16b+14c), which can be calculated from the balance coefficient of the chemical reaction equation. The CO produced by the anaerobic reaction of organic matter in the water body 2 The emission intensity is N·44·(nc-sd / 5-ed / 8), CH 4 The emission intensity is N·16·ed / 8.

[0030] Preferably, the step S3 is specifically as follows: if the carbon emission intensity generated during the hydrolysis of organic matter in the sewage network is to be calculated, the total organic carbon concentration and organic matter (C n Ha O b N c ) concentration and the total organic carbon concentration conversion coefficient, the present invention adopts an experimental method to accurately measure the numerical values ​​of the two boundary conditions.

[0031] Total organic carbon concentration (TOC) and organic matter (C n H a O b N c ) Experimental method for conversion coefficient (S): Total organic carbon concentration is measured according to the method in "Water and Wastewater Monitoring and Analysis Methods" (4th edition), organic matter (C n H a O b N c ) The conversion coefficient (S) can be obtained by first using gas chromatography-mass spectrometry to measure the content of three major categories of substances: carbohydrates, proteins, and fatty acids, and then dividing the total content of the three major categories of substances by the total organic carbon concentration.

[0032] The experimental method for the proportion of organic matter converted into microorganisms (s) is as follows: put the bottom mud and water sample from the sewage network into a closed container, and measure the CH above the container after each reaction period. 4 and CO 2 Content, waiting for CH 4 and CO 2 The content is stable. The total carbon content in the exhaust gas is compared with the total organic carbon content in the water sample to obtain the proportion of organic matter converted into methane (e). 1 minus e can be used to obtain the proportion of organic matter converted into microorganisms (s).

[0033] Preferably, the step S4 is specifically as follows: anaerobic reaction in the sewage pipe network will cause hydrolysis of organic matter and degradation of microorganisms to produce carbon dioxide and methane. The above chemical reaction formula reflects the hydrolysis of organic matter on the one hand, and the degradation of microorganisms (C 5 H 7 O 2 N) is produced. Microorganisms will produce CH through endogenous respiration. 4 and CO 2 , the general formula of endogenous respiratory reaction of microorganisms can be expressed as

[0034]

[0035] M 降解 =HRT×MLVSS×K 0

[0036] Where: M 降解 — Endogenous respiratory degradation microorganisms (C 5 H 7 O 2N) mass, mg / L;

[0037] HRT—hydraulic retention time, d;

[0038] MLVSS—mixed liquor volatile suspended solids concentration, mg / L;

[0039] K 0 —Anaerobic endogenous respiration attenuation coefficient, d -1 .

[0040] Endogenous respiratory degradation microorganisms (C 5 H 7 O 2 N) has a mass of M 降解 , from the chemical reaction equation balance coefficient, we can get CO 2 The emission intensity is 0.584M 降解 , CH 4 The emission intensity is 0.354M 降解 .

[0041] Preferably, step S5 is specifically as follows: if the carbon emission intensity generated in the process of endogenous respiration of organic matter by microorganisms in the sewage pipe network is to be calculated, the volatile suspended solids concentration MLVSS of the mixed liquor and the anaerobic endogenous respiration attenuation coefficient K 0 Two key parameters, the present invention explores the method of laboratory simulation experiment to accurately measure the values ​​of the two key parameters under different conditions.

[0042] The experimental method for mixed liquor volatile suspended solids concentration (MLVSS) is as follows: the organic matter in the sediment sample is oxidized into water and carbon dioxide by high temperature combustion, and then the weight of the residual material is weighed. The MLVSS is obtained by subtracting the ash mass from the mass before combustion and dividing it by the volume.

[0043] Anaerobic endogenous respiration decay coefficient (K 0 ) experimental method: Anaerobic endogenous respiration can follow the Fitzhugh kinetic model, that is, B t =B 0 ·[1-exp(-K 0 By plotting the cumulative methane production (mL / g·MLVSS) versus time (t) on day t, the anaerobic endogenous respiration decay coefficient (K) was calculated by curve fitting. 0 ) measurement value.

[0044] Preferably, the step S6 is specifically as follows: the anaerobic reaction of organic matter in the water and sediment in the sewage pipe network can produce CO 2 and CH 4 , so CO 2 and CH 4The emission intensity is the sum of the water body emission intensity and the sediment emission intensity, that is, CO 2 The total emission intensity is N·44·(nc-sd / 5-ed / 8)+0.584M 降解 , CH 4 The total emission intensity is N·16·ed / 8+0.354M 降解 .

[0045] 3. Beneficial effects

[0046] Compared with the prior art, the beneficial effects of the present invention are as follows: the present invention proposes a method for calculating the carbon emission intensity of a sewage network that combines anaerobic reaction theory with the material balance method, which can be used for carbon emission accounting of a sewage network under different boundary conditions. Compared with the emission factor method and the actual measurement method, the method has stronger applicability and higher accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 It is a flow chart of the present invention;

[0048] Figure 2 The cumulative methane production versus time is used to measure the endogenous respiration decay coefficient (K 0 );

[0049] Figure 3 The figure below is a comparison of the calculated and measured carbon emission intensity of the sewage network. 2 Comparison chart of calculated and measured values, the right picture is CH 4 Comparison chart of calculated and measured values. DETAILED DESCRIPTION

[0050] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings and embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0051] Reference Figure 1 , a method for calculating the carbon emission intensity of a sewage network based on anaerobic reaction theory is as follows:

[0052] The first step is to use gas chromatography-mass spectrometry to measure the content of sugar, protein and oil pollutants in the sewage pipe network. In this embodiment, sugar (C 6 H 5 O 5 ), protein (C 16 H 24 O 5 N 4 ) and oils (C 16 H32 O 2 ) The pollutant ratio is 1:1:1. Through measurement, it can be known that the total molecular formula of organic matter in the sewage pipe network is C 38 H 61 O 12 N 4 The anaerobic reaction mainly includes three stages. The first stage is the hydrolysis and acidification stage, which mainly decomposes macromolecular organic matter into higher fatty acids under the action of microbial extracellular enzymes, such as fatty acid alcohols from sugars, fatty acid amines from proteins, and short-chain fatty acid pyruvic acid from oils and fats. The second stage is the hydrogen and acetic acid production stage. Under the action of hydrogen and acetic acid producing microorganisms, the various organic acids produced in the first stage are decomposed and converted into acetic acid and H 2 The third stage is the methanogenic stage, in which methanogenic microorganisms convert acetic acid, acetate, and CO 2 and H 2 etc. are converted into methane.

[0053] The second step is to obtain the organic matter (C 38 H 61 O 12 N 4 )The chemical reaction formula of the anaerobic reaction process is as follows:

[0054]

[0055] In the third step, in this embodiment, the total organic carbon concentrations of the inlet and outlet water of the sewage pipe network are 73.56 mg / L and 71.38 mg / L respectively, and the conversion coefficients are 0.65 and 0.62 respectively. The organic matter (C 38 H 61 O 12 N 4 ) reduction was 3.56mg / L, organic matter (C 38 H 61 O 12 N 4 ) relative molecular weight 765, the amount of reduction converted to the amount of substance is 4.65×10 -6 mol / L. The experimental results show that the proportion of organic matter converted into microorganisms (s) is 0.12, and the proportion of organic matter converted into methane (e) is 0.88. The balance coefficient of the chemical reaction equation can be used to calculate the CO generated by the anaerobic reaction of organic matter in the water. 2 The emission intensity is 2.104 mg / L, CH 4 The emission intensity is 1.449 mg / L.

[0056] Step 4: In the embodiment, the hydraulic retention time (HRT) of the pipe network is 0.085 d, which can be calculated from the sediment endogenous respiration model.2 The emission intensity is 0.04964·MLVSS·K 0 , CH 4 The emission intensity is 0.03009·MLVSS·K 0 .

[0057] Step 5: ① Dry the quantitative filter paper at 103-105℃, cool it during the drying period, and weigh it. Repeat this process until a constant weight is obtained. The weight is m 0 ② Filter 100 ml of the sample with the filter paper in ①, dry it in an oven at 103-105℃, cool it in a dryer to the equilibrium temperature, and weigh it. The weight is m 1 ③Put the clean crucible in an oven and dry it for one hour, take it out and cool it to the equilibrium temperature in a desiccator, and weigh it. The weight is m 2 ④Put the filter paper and mud in ② into the crucible in ③, and then put it into a cold muffle furnace, heat it to 600℃ and burn it for 120 minutes, cool it to the equilibrium temperature in a desiccator, and weigh it. The weight is m 3 According to the calculation formula MLVSS = [(m 1 +m 2 -m 0 )-m 3 ] / 0.1, and perform MLVSS calculation. In this embodiment, m 0 is 1.3552 g, m 1 153.6364g, m 2 85.7924g, m 3 It is 237.9338g, and the calculated MLVSS is 1398mg / L.

[0058] Anaerobic endogenous respiration decay coefficient (K 0 ) By plotting the cumulative methane production (mL / g·MLVSS) versus time (t) on day t, the anaerobic endogenous respiration decay coefficient (K) can be calculated by curve fitting. 0 ) The measured value is 0.128d -1 The parameters of mixed liquor volatile suspended solids concentration (MLVSS) and endogenous respiration attenuation coefficient (K 0 ) measured value, the sediment CO 2 The emission intensity is 8.883 mg / L, CH 4 The emission intensity is 5.384 mg / L.

[0059] Step 6: CO2 reduction in sewage pipe network based on anaerobic reaction theory 2 The total emission intensity is 10.987 mg / L, CH 4 The total emission intensity is 6.833 mg / L.

[0060] Select 8 sewage pipe networks CO 2 and CH 4 The measured value of the emission flux is compared with the calculated value using this method. The comparison chart between the measured value and the calculated value is as follows. The error analysis shows that the error of calculating the carbon emission intensity of the sewage network using this method is within 25%, and the accuracy is relatively high.

Claims

1. A method for calculating the carbon emission intensity of sewage pipe network based on anaerobic reaction theory. It is characterized in that The following steps are involved: S1: Determine the biochemical reaction process of organic matter in the sewage pipe; S2: Calculate the carbon emission intensity of water bodies by chemical reaction equation; S3: Experimentally determine the water quality and key parameters required for calculation; S4: Calculate sediment carbon emission intensity using the anaerobic endogenous respiration reaction equation; S5: Laboratory simulation experiments to determine the key parameters of the sediment endogenous model; S6: Calculate the overall carbon emission intensity of the pipeline network based on the anaerobic reaction process; The step S1 specifically includes: determining the composition of pollutants in the sewage pipe, including the content of sugar, protein and oil pollutants, and their chemical formulas; determining the biochemical reaction process of the sewage pipe in the area according to the chemical formula; The step S2 specifically includes: some organic matter in the sewage participates in anaerobic reaction to generate methane, some organic matter is used for the growth of microorganisms, and organic matter C n H a O b N c The general chemical reaction formula of the anaerobic reaction process is expressed as: The symbols and values ​​in brackets in the above formula are the equilibrium coefficients of the reaction; where: d = 4n + a-2b-3c; s is the portion of organic matter converted into microorganisms; e is the portion of organic matter converted into methane; s + e = 1, and the value of s varies with the composition of organic matter, microbial community structure and metabolic activity. The specific value is determined based on laboratory simulation experiments and can also be estimated based on the following formula: s=0.2a e Where: 0.2 is the coefficient of non-degradability of microorganisms; a e is the maximum coefficient value of organic matter converted into microorganisms; Anaerobic reactions of several pollutants e Value, ratio calculated by COD, as shown in Table 1; Table 1 Anaerobic reaction of several pollutants e value The total organic carbon concentrations at the inlet and outlet of the sewage network are TOC in and TOC out , the conversion coefficients are S in and S out , organic matter C n H a O b N c The reduction amount is converted by TOC reduction amount and conversion coefficient, Δm = S in ·TOC in -S out ·TOC out ; From organic matter C n H a O b N c Relative molecular weight, converted into the amount of substance N = Δm / (12n+a+16b+14c), is calculated from the balance coefficient of the chemical reaction equation. CO produced by the anaerobic reaction of organic matter in the water 2 The emission intensity is N·44·(nc-sd / 5-ed / 8), CH 4 The emission intensity is N·16·ed / 8; The step S3 is specifically as follows: if the carbon emission intensity generated during the hydrolysis of organic matter in the sewage network is to be calculated, the total organic carbon concentration and the organic matter C n H a O b N c The two boundary conditions of concentration and total organic carbon concentration conversion coefficient are measured accurately by experimental method. Total organic carbon concentration TOC and organic matter C n H a O b N c Experimental method for conversion coefficient S: organic matter C n H a O b N c The conversion coefficient S is measured by first using a gas chromatography-mass spectrometry (GC-MS) instrument to determine the contents of three major types of substances, namely sugars, proteins, and fatty acids, and then dividing the total content of the three major types of substances by the total organic carbon concentration to obtain the conversion coefficient S; The experimental method for measuring the proportion of organic matter converted into microorganisms is as follows: put the bottom mud and water sample from the sewage network into a closed container, and measure the CH 4 and CO 2 Content, waiting for CH 4 and CO 2 The content is stable. Compare the total carbon content in the exhaust gas with the total organic carbon content in the water sample to obtain the proportion of organic matter converted into methane, e. Subtract e from 1 to obtain the proportion of organic matter converted into microorganisms, s. The specific content of step S4 is as follows: In the sewage pipe network, anaerobic reactions will occur in the hydrolysis of organic matter and microbial degradation, generating carbon dioxide and methane; on the one hand, it reflects the hydrolysis of organic matter, and on the other hand, it reflects the generation of C 5 H 7 O 2 N; microorganisms will undergo endogenous respiration and finally generate CH 4 and CO 2 . The general formula for the endogenous respiration reaction of microorganisms is expressed as: M degradation = HRT × MLVSS × K 0 Where: M 降解 Microorganisms that degrade endogenous respiration C 5 H 7 O 2 N mass, mg / L; HRT is hydraulic retention time, d; MLVSS is the volatile suspended solids concentration of the mixed liquor, mg / L; K 0 is the anaerobic endogenous respiration attenuation coefficient, d -1 ; Endogenous respiratory degradation microorganisms C 5 H 7 O 2 N has a mass of M 降解 , from the chemical reaction equation balance coefficient, we get CO 2 The emission intensity is 0.584M 降解 , CH 4 The emission intensity is 0.354M 降解 ; The step S5 is specifically as follows: if the carbon emission intensity generated in the process of endogenous respiration of organic matter by microorganisms in the sewage pipe network is to be calculated, the volatile suspended solids concentration MLVSS of the mixed liquid and the anaerobic endogenous respiration attenuation coefficient K 0 Two key parameters, using the laboratory simulation experiment method, accurately measure the values ​​of the two key parameters under different conditions; Experimental method for mixed liquor volatile suspended solids concentration (MLVSS): high temperature combustion is used to oxidize organic matter in sediment samples into water and carbon dioxide, and then the weight of the residual material is weighed. MLVSS is obtained by subtracting the ash mass from the mass before combustion and dividing by the volume. Anaerobic endogenous respiration decay coefficient K 0 Experimental method: Anaerobic endogenous respiration follows the Fitzhugh kinetic model, that is, B t =B 0 ·[1-exp(-K 0 ·t)]; by plotting the cumulative methane production mL / g·MLVSS on day t versus time t, the anaerobic endogenous respiration attenuation coefficient K was calculated by curve fitting. 0 Measurement value; The step S6 is specifically as follows: the anaerobic reaction of organic matter in the water and sediment in the sewage pipe network can produce CO 2 and CH 4 , so CO 2 and CH 4 The emission intensity is the sum of the water body emission intensity and the sediment emission intensity, that is, CO 2 The total emission intensity is N·44·(nc-sd / 5-ed / 8)+0.584M 降解 , CH 4 The total emission intensity is N·16·ed / 8+0.354M 降解 .

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